1. Field of the Invention
The present invention relates to a cable network, and more particularly, to a media access control (MAC) frame structure and a data communication method for reducing various signaling processes required in case that a cable modem (CM) wishes to change a header format of a suppressed packet.
2. Description of the Background Art
A cable network, which is a form of media for providing various multimedia services such as an analog signal, a data signal, and audio and moving picture signals, has been spread all over the world.
The cable network is divided into a cable modem (CM) for helping a user transmit and receive a data and a cable modem terminal system (CMTS) connected to a wide area network for transmitting a data to a user and receiving a data from a user through a radio-wave repeater station.
The CM has great possibilities in a cable network field with the development of the Internet.
The multimedia cable network system partners (MCNS) that currently lead cable services all over the world established cable television laboratories referred to as “Cable Labs” and have executed a cable modem project referred to as data-over-cable service interface specifications (DOCSIS). The Annex B, which is one of the standards of the CM recommended by the international telecommunications union-telecommunication standardization sector (ITU-T) in 1998, adopts the DOCSIS 1.0 specification created by the MCNS that is a cable television enterpriser group of North America. The DOCSIS version 1.1 has currently been published.
In the North America standards that have currently been developed by the enterprises all over the world, the CM performs only a bridging function of transmitting an Internet protocol (IP). However, the CM acquires the IP and the configuration files thereof or has an upper communication protocol for operating as a simple network management protocol agent. The required standards of the CM have been defined through the configuration files in order to transmit data at very high speed on a cable television network.
The DOCSIS provides the following characteristic functions in order to guarantee quality of service (QoS) the same as the QoS of voice over IP (VoIP).
1. Dynamic service flow establishment
2. Upstream service flow scheduling service
3. Fragmentation
4. Payload header suppression (PHS)
Herein, the PHS means that, when a sender suppresses (conceals) the unnecessary parts that need not be repeatedly transmitted in a payload header of a media access control (MAC) frame and transmits the remaining parts, a receiver restores the concealed parts and transmits the restored parts to a third receiver. In communication in an upstream direction, the sender is the CM and the receiver is the CMTS. In communication in a downstream direction, the sender is the CMTS and the receiver is the CM. The position where the suppression is performed is the end of an extended header and comes after a header check sequence (HCS) field.
The above contents will now be described in more detail.
FIG. 1 shows a MAC frame according to a conventional art. As shown in FIG. 1, the suppression is performed in a payload data unit (PDU) data stream, which is the end of an extended header and is positioned after the HCS field in a transmitted data string, and is repeatedly applied to a specific field in the transmitted payload header of the PDU data of the MAC frame.
At this time, a payload header suppression index (PHSI) is included in the EH_VALUE of the extended header (EHDR). The PHSI is an index that denotes a payload header suppression field (PHSF). The PHSF is a string that denotes the header of the PDU suppressed more than 1 byte. The PHSI of 8 bits is unique in each service identifier (SID) in the upstream direction and in each CM in the downstream direction and is designated by the CMTS.
As shown in FIG. 1, a destination address (DA) means the address of the receiver, to which a packet is to be transmitted, in a suppressed payload header field. A source address (SA) means the address of the sender. User data means the actual data of a user to be transmitted to the receiver.
Packet transmission between the sender and the receiver will now be described in more detail.
First of all, the sender classifies a packet to be transmitted using a classifier and transmits the packet in an appropriate service flow. At this time, the classifier suppresses a specific payload header field of the packet using the PHSI mapped to the classifier and using the payload header suppression (PHS) rule of the PHSI.
During the suppression of the payload header, parameters according to the PHS rule that is defined in the sender and the receiver and is used by the sender and the receiver include the PHSF, the PHSI, a payload header suppression mask (PHSM), a payload header suppression size (PHSS), and payload header suppression verification (PHSV). Here, the PHSM is a bit mask for determining whether the PHSF is suppressed, that is, a parameter for determining which byte of the PHSF is to be suppressed and which byte of the PHSF is not to be suppressed. The PHSS is the length of the total suppressed bytes and has the value equal to the number of bytes of the PHSF to be transmitted. Also, the PHSV is a flag for comparing all of the bytes suppressed by a sender entity with an original header byte before transmitting all of the bytes suppressed by the sender entity, to thus show whether to examine all of the bytes suppressed by the sender.
The CM which is the sender in the upstream direction compares the original header byte for the suppression with the byte of the PHSF designated as a suppression region by the PHSM and performs the suppression when the original header byte coincides with the byte of the PHSF. The CM that is the sender inserts the PHSI into the EH_VALUE and transmits the packet according to the designated upstream service flow. The CMTS that is the receiver searches the PHSF, the PHSM, and the PHSS through the SID and the PHSI of the packet and restores an original packet using the byte included in the PHSF.
A rule for data transmission and reception between the sender and the receiver is necessary for the sender and the receiver to smoothly perform payload header suppression. The rule is the PHS rule. The PHS rule is generated through a registration message, a dynamic service addition (DSA) message, and a dynamic service change (DSC) message and is deleted through the DSC message and a dynamic service deletion (DSD) message. Here, when the PHS rule is generated, the CMTS defines the PHSI.
The DSA, the DSC, and the DSD are dynamic signaling standards for defining the contents of programming of channel characteristics, change in the channel characteristics, and deletion of the programmed channel characteristics and are provided by the DOCSIS version 1.1.
The PHS rule is partially or completely defined through the DSA message, the DSC message, and the DSD message when a service flow is generated.
FIG. 2 is a block diagram describing a data communication method in the cable network according to the conventional art. The parameters according to the partially generated PHS rule are changed through 3 steps of exchanging DSC-REQ, DSC-RSP, and DSC-ACK messages between a CM 10 and a CMTS 20, which are DSC signaling processes.
In step 1, the CM 10 encodes the PHSS and the PHSF, loads the encoded PHSS and PHSF on the DSC-REQ message, and transmits the PHSS and the PHSF, which are loaded on the DSC-REQ message, to the CMTS 20 since the PHSS and the PHSF are not defined in the PHS rule.
In step 2, the CMTS 20 checks whether there exist errors in the transmitted parameters and transmits the DSC-RSP message showing whether the requested PHS rule can be supported to the CM 10.
In step 3, when the CM 10 transmits the received response of the DSCRSP to the CMTS 20 through the DSC-ACK message again, communication setting according to all of the DSC signaling processes is terminated.
In the step 1, during the initialization of the configuration file, the PHSF and the PHSS are not defined among the parameters of the PHS rule. The PHS rule is partially defined. In the step 2, when the parameter values of the channel are changed through the DSC signaling, the PHS rule previously registered or partially generated through the DSA is completely defined due to the changed parameters of the channel.
As mentioned above, according to the MAC frame structure and the data communication method in the cable network according to the conventional art, when a mode of the service flow generated through the registration process or DSA signaling is activated, in the case where complicated DSC signaling is used in order to simply change the PHS rule parameter, time is delayed and all of the bandwidths of the cable network are used for the DSC signaling. Accordingly, the efficiency of resources deteriorates.